OTWO,
I agree that it's probably rare to literally get up and walk out in the middle of a meeting. In my case, there were many many things that I found troubling within the organization in the nearly 60 years I was in but I took them to be allowed by J as a test of loyalty. That's what is drummed into the flock by the GB.
Yet, over time these things continue to pile up higher and higher until just one more straw breaks the cart. It doesn't even have to be big- just one too many. If it just so happens to be said or done at a meeting..... well out you go.